1. Field of the Invention
The present invention generally relates to a substrate detecting system and, more particularly, to a system for performing detection processing for the presence/absence of a base material or a wafer of a semiconductor device or a liquid crystal display device (LCD) including a transparent substrate.
2. Description of the Related Art
In a general process for manufacturing a semiconductor device or a liquid crystal display device (LCD), a predetermined number of wafers or base materials are accommodated in a vessel called a cassette (carrier), and they are moved through various steps. In every step, detection processing is performed about the presence/absence of the wafers or base materials
For example, a conventional detecting system for detecting the presence/absence of a large number of wafers accommodated in a carrier used in a semiconductor manufacturing process includes optical detecting units, the number of which is the number of wafers to be accommodated. That is, one of the wafer detecting apparatuses causes a light-receiving element to receive an infrared beam radiated from a light-emitting element such as a light-emitting diode (LED) so as to detect the presence/absence of a wafer (the infrared beam is interrupted due to the presence of the wafer and not received by the light-receiving element). In another conventional wafer detecting apparatus, a non-contact detecting method is employed. That is, in this method, a laser beam is radiated onto a wafer, and the beam reflected by the wafer is received, thereby detecting the presence/absence of a wafer (the reflected beam is not received without the presence of a wafer).
In recent years, a transparent substrate made of quarts glass is often used as a wafer or substrate in a certain type semiconductor device or liquid crystal display device (LCD). However, since a radiation beam or laser beam from the light-emitting element of a conventional optical detecting apparatus is transmitted through the transparent wafer or substrate, a beam to be received by a light-receiving element is not interrupted by the presence of the wafer or substrate, and the optical detecting apparatus cannot detect the presence/absence of the wafer or substrate. For this reason, the following contact detecting method or the like is employed. In this method, the wafer or substrate is brought into contact with a member having a spring, and the spring is contracted by the weight of the wafer or substrate to operate a microswitch, thereby detecting the presence/absence of the wafer or substrate.
In detection of the wafer or substrate using the contact detecting method, the wafer is easily damaged at its contact portion. In addition, in some step, a thin film formed on the wafer may be removed to easily produce dust or particles, thereby inevitably forming a contamination source. Therefore, the yield of finished semiconductor elements or liquid crystal display devices (LCD) is disadvantageously decreased.